This invention relates to improved methods for treating phosphatide-containing mixtures. More particularly, this invention relates to methods for recovering purified vegetable oil, aqueous organic acid, and organic acid-treated phosphatide from a phosphatide-containing mixture comprising an acid-and-oil mixture obtained from organic acid refining of vegetable oil.
Vegetable oils are typically obtained by pressing or extracting the oil seeds of plants such as corn or soybeans. Properly processed vegetable oils are suitable for use in many edible oil and fat compositions destined for human consumption. Such edible oils and fats include salad oils, cooking oils, frying fats, baking shortenings, and margerines. In addition to being widely used in edible oils and fats, vegetable oils are also increasingly utilized in important industrial products such as caulking compounds, disinfectants, fungicides, printing inks, and plasticizers.
Vegetable oils primarily consist of triglycerides, also termed triacylglycerols. In addition to triglycerides, however, vegetable oils also contain several other compounds. Some of these additional compounds, such as mono- and di-glycerides, tocopherols, sterols, and sterol esters, need not necessarily be removed during processing. Other compounds and impurities such as phosphatides, free fatty acids, odiferous volatiles, colorants, waxes, and metal compounds negatively affect taste, smell, appearance and storage stability of the refined oil, and hence must be removed. Carefully separated, however, some of these additional compounds, particularly the phosphatides, are valuable raw materials. It is therefore important to select a vegetable oil purifying method that maximizes removal of impurities but does so in a way that least impacts the compounds removed.
Vegetable oil triglycerides are esters of 1,2,3-propane triol, and can be represented by the generic formula 
where R1, R2, and R3 are the same or different, and are selected from the group consisting of C10-C22 saturated and unsaturated fatty acids. In soybean oil in particular, the saturated fatty acids that can occur include but are not limited to lauric (C12:0), myristic (C14:0), palmitic (C16:0), stearic (C18:0), arachidic (C20:0), and behenic (C22:0) acids. Generally, however, the fatty acids of soybean oil are predominantly unsaturated, and include but are not limited to oleic (C18:1), linoleic (C18:2), and linolenic (C18:3) acids. Unsaturated fatty acids can exist as geometric and/or positional isomers, each such isomer having different properties such as melting point. Naturally occurring fatty acids generally exist in the cis form, but they can be converted into the trans form during the course of purification steps used to produce a vegetable oil from an oilseed. Crude soybean oil in particular typically contains from about 95 to about 97 percent by weight triglycerides.
The terms phosphatides and phosphatide concentrates are commonly used to refer to a mixture of phospholipids comprising phosphatidyl derivatives which are present in crude vegetable oil. Phosphatides are also called gums, wet gums, lecithin, and wet lecithin. The term lecithin, from a true chemical sense, refers to phosphatidyl choline. However, as used by commercial suppliers, the term lecithin refers to a product derived from vegetable oils, especially soybean oil. Specific chemical components of phosphatides present in vegetable oil include phosphatidyl choline, 1; phosphatidylethanolamine, 2; phosphatidylinositol, 3; phosphatidyl serine, 4; phosphatidic acid, 5; cyclolipids, and other components such as free sugars, metals and free fatty acids. 
Such phosphatides are amphipathic, i.e., one end of the molecule is hydrophilic (lipophobic) and the other end is hydrophobic (lipophilic). As a result, they possess useful surface-active properties, and can orient in aqueous environments to create membranes and bilayers.
The fatty acid content of the phosphatides 1 through 5 is represented by R1 and R2, as defined above, and generally matches that of the vegetable oil from which they are derived. The phosphatide content of vegetable oil will vary based on a number of factors, including but not limited to oilseed type, seed quality, and the process by which oil is extracted therefrom. Crude soybean oil in particular typically contains from about 1.5 to about 3 percent by weight phosphatides. Phosphatides comprise both hydratable phosphatides (HPs) and non-hydratable phosphatides (NHPs). Although non-hydratable phosphatides tend to remain oil-soluble and are largely unaffected by water, hydratable phosphatides when hydrated become greater in density than the triglycerides and precipitate, or settle out. This phenomenon forms the basis for the process of conventional water degumming, discussed more fully below.
Vegetable oil impurities are typically removed in four distinct steps of degumming, refining, bleaching, and deodorizing. Of these four steps, degumming removes the largest amount of impurities, the bulk of which are hydratable phosphatides. Refining primarily removes non-hydratable phosphatides, soaps created from the neutralization of free fatty acids, and other impurities such as metals. Bleaching then improves the color and flavor of refined oil by decomposing peroxides and removing oxidation products, trace phosphatides, and trace soaps. Soybean oil bleaching materials include neutral earth (commonly termed natural clay or fuller""s earth), acid-activated earth, activated carbon, and silicates. Deodorizing is the final processing step and prepares the oil for use as an ingredient in many edible products including salad oils, cooking oils, frying fats, baking shortenings, and margerines. The deodorizing process generally comprises passing steam through refined oil at high temperature and under near vacuum conditions to vaporize and carry away objectionable volatile components.
Vegetable oil refining, also known as neutralization or deacidification, essentially involves removing free fatty acids (FFA) and phosphatides from the vegetable oil. Most refining operations employ either alkali refining (also termed caustic refining) or physical refining (also termed steam refining). Of these two refining methods, alkali refining predominates.
For either refining method, an optional but preferred first step is a conventional water degumming process. Degumming refers to the process of removing hydratable phosphatides and other impurities such as metals from vegetable oils. A simple degumming process comprises admixing soft water with the vegetable oil and separating the resulting mixture into an oil component and an oil-insoluble hydrated phosphatides component (frequently referred to as a xe2x80x9cwet gumxe2x80x9d or xe2x80x9cwet lecithinxe2x80x9d). The NHPs, generally considered to be calcium and magnesium salts of phosphatidic acids, are largely unaffected by water and remain soluble in the oil component. Phosphatidic acids are typically produced via the action of phospholipidase D, which splits off the non-fatty-acid moiety from phospholipids.
Normally, refiners also must introduce chelating agents following degumming processes to remove metal compounds from crude vegetable oil, which typically contains calcium, potassium, magnesium, aluminum, iron and copper. Left in place, these metal impurities form salts of phosphatidic acid, thereby contributing to the NHP content. Moreover, metal contaminants, especially iron, can darken oil during deodorization, and even small amounts of iron that do not affect the oil""s color can nevertheless dramatically reduce stability of refined oil.
Treating crude vegetable oil with soft water produces a degummed oil and a phosphatide concentrate containing the hydratable phosphatide fraction. This phosphatide concentrate subsequently can be removed from the degummed oil by a convenient method such as by gravitational force or by centrifugal separation. Phosphatide concentrates coming from centrifugal separation will generally contain up to about fifty percent by weight water, and typically will contain from about twenty-five to about thirty percent by weight water. In order to minimize chances of microbial contamination, phosphatide concentrates must be dried or otherwise treated immediately. Dried phosphatide concentrates can be profitably sold as commercial lecithin. Degummed oil is further refined to remove NHPs and other unwanted compounds.
Mineral acid also is sometimes added during the water degumming process to help minimize the NHP content of degummed oil. The acid combines with calcium and magnesium salts, enabling phosphatidic acids to migrate from the oil to the water phase, thus eliminating them from the crude oil. However, using mineral acid during degumming is inappropriate when seeking to recover gums intended for use as lecithin because the presence of mineral acid will cause darkening of the lecithin.
In alkali refining, free fatty acids and gums are removed from crude or degummed oil by mixing the oil with a hot, aqueous alkali solution, producing a mixture of so-called neutral oil and soapstock (also termed refining byproduct lipid), which is an alkaline mixture of saponified free fatty acids and gums. The neutral oil is then separated from the soapstock, typically by centrifugation. The soapstock has commerical value due to its fatty acid content but must be processed further in order to render it salable. The neutral oil is further processed to remove residual soap.
Soapstock is treated in a process called acidulation, which involves breaking or splitting the soap into separate oil and aqueous phases through addition of a mineral acid such as sulfuric acid to reduce the pH to approximately 1.5, followed by thorough heating and mixing. Because the aqueous phase is heavier than the oil phase, the acidulated soapstock is separated from the oil by gravity or centrifugation. The separated oil (termed acid oil) has essentially the composition of the neutral oil and is drawn off, washed with water to completely remove mineral acid and sludge, and sold, usually as an animal feed supplement. The remaining aqueous phase (termed acid water) is the final waste product and must be neutralized before being discarded.
The alkali refining process has several drawbacks, however. One drawback is that alkali refining requires large amounts of high-quality water and creates a correspondingly high amount of wastewater that creates expensive and troublesome disposal concerns. For example, in preparing the aqueous alkali and aqueous mineral acid solutions used in alkali refining, the required water must be demineralized to prevent conversion of HPs into NHPs. In separating neutral oil from soapstock, centrifugation alone is insufficient to completely remove soapstock, and thus a demineralized water wash at a rate of about 10 to 12 percent by weight of the feed is required to aid separation of soapstock. In acidulating the soapstock, which by this time comprises about 50 percent by weight water, aqueous mineral acid must be used in considerable excess, thereby contributing even more water. A typical alkali refining operation requires a demineralized water usage rate of about 0.1 times the amount of oil being treated.
Having then incurred the cost of using large amounts of high-quality water, alkali refiners essentially throw that water investment away in the form of an acid water waste stream, disposal of which is even then only possible after having incurred further additional costs relating to pollution control. The acid water created during soapstock splitting is high in biochemical oxygen demand (BOD) and low in pH. Disposal regulations require at minimum that the acid water be neutralized before the waste can be dumped. Many states have much more stringent pollution controls, requiring often costly solutions to ensure effluent biodegradability.
Another drawback is refining losses that occur due to the soapstock""s emulsifying effect, wherein soapstock acts to take up a portion of the valuable neutral oil into the aqueous soapstock solution. To minimize such emulsification losses, the crude or degummed oil is usually heated to between 158xc2x0 F. and 194xc2x0 F. prior to being contacted with the hot alkali solution. However, heating will not completely prevent emulsions from forming, nor will it entirely break emulsions once formed. Centrifugation forces also are insufficient to completely break emulsions of neutral oil in soapstock.
An additional drawback to alkali refining is losses that occur when a portion of the neutral oil undergoes alkaline hydrolysis, often referred to as saponification, to produce undesirable fatty acid salts. Allowing the alkali solution and the crude or degummed oil to remain in contact for only short times can minimize saponification losses but is often insufficient to remove impurities other than fatty acids, especially impurities such as phosphatides and metal compounds. Consequently, short contact times can make it necessary to conduct a second round of refining.
Yet another alkali refining drawback is that raw soapstock is troublesome to handle. Soapstock solidifies quickly upon cooling, so heated holding tanks and transfer lines are required to maintain temperatures above 140xc2x0 F. Elevated temperatures also are required to prevent fermentation. On the other hand, overly heating soapstock causes it to boil, producing excessive and troublesome foaming.
Thus, alkali refining involves many processing steps and has many drawbacks. In attempting to address the problems associated with alkali refining, operators must simultaneously vary many factors including the amount of heat applied, the amount and concentration of alkali, and retention times. Successfully balancing all these factors is a complex and difficult task. Furthermore, successful balancing of factors nevertheless can leave the need for additional refining cycles.
An alternative to alkali refining is physical refining. Physical refining is a steam distillation process essentially the same as that used in conventional vegetable oil deodorization processes, in which steam passing through vegetable oil vaporizes and carries away free fatty acids. The main advantage of physical refining over alkali refining is that no soapstock is generated. A second advantage is lower refining losses because there is no saponification of oil and no oil entrainment and/or emulsification by soapstock.
Accordingly, there is significant interest in physical refining due to its economic advantages and friendliness compared to alkali refining. But because physical refining does not remove NHPs, any oils to be physically refined must be free of NHPs in order to ensure stable refined oils. Oils such as palm oil and tallow, which have low NHP content, can be successfully physically refined. But oils such as soybean oil and sunflower seed oil, which are relatively high in NHPs, are not commonly physically refined because the pre-refining step of water degumming does not remove NHPs. Moreover, physically refined soybean oils have only limited acceptance in the U.S. market due to their lack of flavor stability.
Thus, although present methods exist for refining vegetable oils, significant drawbacks remain. Alkali refining can substantially remove phosphatides and other impurities but presents economic challenges and water pollution concerns. Physical refining is economically and environmentally less challenging, but many vegetable oils including soybean oil which are high in NHPs cannot be acceptably physically refined.
Consequently, further improvements in purifying vegetable oil, and especially soybean oil, have been sought, particularly with regard to obtaining purified vegetable oil low in free fatty acids, phosphatides, and other impurities such as metals in an environmentally friendly manner. The present invention relates to an improved process having advantages over those previously disclosed. In particular, this invention relates to improved methods for treating phosphatide-containing mixtures.
One aspect of the present invention relates to an improved process for treating phosphatide-containing mixtures. An improved process of the present invention effectively recovers purified vegetable oil, aqueous organic acid, and organic acid-treated phosphatide from a phosphatide-containing mixture comprising an acid-and-oil mixture obtained from organic acid refining of vegetable oil.
Another aspect of the invention relates to an improved process for treating phosphatide-containing mixtures that produces an environmentally friendly aqueous organic acid phase that can be recovered and used without subsequent processing, thereby allowing the water used in organic acid refining to be nearly completely recycled.
One embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase and a phosphatide-enriched aqueous phase; and removing the purified vegetable oil phase.
Another embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase and a phosphatide-enriched aqueous phase; removing the purified vegetable oil phase; separating the phosphatide-enriched aqueous phase into an aqueous organic acid phase and an organic acid-treated phosphatide phase; and removing either the aqueous organic acid phase or the organic acid-treated phosphatide phase.
Yet another embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase and a phosphatide-enriched aqueous phase; removing the purified vegetable oil phase; separating the phosphatide-enriched aqueous phase into an aqueous organic acid phase and an organic acid-treated phosphatide phase; removing either the aqueous organic acid phase or the organic acid-treated phosphatide phase; and recycling the aqueous organic acid phase into the organic acid refining process.
A further embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase, an aqueous organic acid phase, and an organic acid-treated phosphatide phase; and removing the purified vegetable oil phase.
A still further embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase, an aqueous organic acid phase, and an organic acid-treated phosphatide phase; removing the purified vegetable oil phase; and removing either the aqueous organic acid phase or the organic acid-treated phase.
An even further embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase, an aqueous organic acid phase, and an organic acid-treated phosphatide phase; removing the purified vegetable oil phase; removing either the aqueous organic acid phase or the organic acid-treated phase; and recycling the aqueous organic acid phase into the organic acid refining process.
A yet further embodiment embodiment of the invention is a process for treating a phosphatide-containing mixture that comprises the steps of providing a phosphatide-containing mixture obtained from an organic acid refining process; separating the phosphatide-containing mixture into a purified vegetable oil phase, an aqueous organic acid phase, and an organic acid-treated phosphatide phase; removing the aqueous organic acid phase; and recycling the aqueous organic acid phase into the organic acid refining process.
These and other aspects of the invention will become apparent in light of the detailed description below.